1. Technical Field
This disclosure relates to servicing a wellbore. More specifically, it relates to self-repairing cement compositions and methods of making and using same.
2. Background
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe (e.g., casing) is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed.
During the productive phase of the wellbore, set cement compositions behind casing are subjected to stresses due to pressure and temperature changes in the wellbore. As a result, the cement sheath may develop cracks internally or debond at the casing or the wellbore creating flow pathways for unwanted fluid migration. Additionally, the cement may also shrink and create microannuli between the casing and the cement and/or the formation and the cement. These processes can result in an increased permeability in the cement and/or the loss of structural integrity of the cement sheath. Repairing cracked or shrunken sheaths may involve techniques such as squeeze cementing which are quite often expensive procedures and adversely affect the production efficiency due to the downtime required. Thus, an ongoing need exists for cement compositions that retain structural integrity.